This is a note to let you know that I've just added the patch titled NFC: reorganize the functions in nci_request to the 4.19-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: nfc-reorganize-the-functions-in-nci_request.patch and it can be found in the queue-4.19 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 2e03efe337dbaa9a553a63a2141af233572583f3 Author: Lin Ma <linma@xxxxxxxxxx> Date: Mon Nov 15 22:56:00 2021 +0800 NFC: reorganize the functions in nci_request [ Upstream commit 86cdf8e38792545161dbe3350a7eced558ba4d15 ] There is a possible data race as shown below: thread-A in nci_request() | thread-B in nci_close_device() | mutex_lock(&ndev->req_lock); test_bit(NCI_UP, &ndev->flags); | ... | test_and_clear_bit(NCI_UP, &ndev->flags) mutex_lock(&ndev->req_lock); | | This race will allow __nci_request() to be awaked while the device is getting removed. Similar to commit e2cb6b891ad2 ("bluetooth: eliminate the potential race condition when removing the HCI controller"). this patch alters the function sequence in nci_request() to prevent the data races between the nci_close_device(). Signed-off-by: Lin Ma <linma@xxxxxxxxxx> Fixes: 6a2968aaf50c ("NFC: basic NCI protocol implementation") Link: https://lore.kernel.org/r/20211115145600.8320-1-linma@xxxxxxxxxx Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/net/nfc/nci/core.c b/net/nfc/nci/core.c index 33c23af6709d4..1008bbbb3af9c 100644 --- a/net/nfc/nci/core.c +++ b/net/nfc/nci/core.c @@ -156,12 +156,15 @@ inline int nci_request(struct nci_dev *ndev, { int rc; - if (!test_bit(NCI_UP, &ndev->flags)) - return -ENETDOWN; - /* Serialize all requests */ mutex_lock(&ndev->req_lock); - rc = __nci_request(ndev, req, opt, timeout); + /* check the state after obtaing the lock against any races + * from nci_close_device when the device gets removed. + */ + if (test_bit(NCI_UP, &ndev->flags)) + rc = __nci_request(ndev, req, opt, timeout); + else + rc = -ENETDOWN; mutex_unlock(&ndev->req_lock); return rc;